Long-term effects on HEK-293 cell line after co-culture with porcine endogenous retrovirus

Characterization of PERV in a new conserved pig herd as potential donor animals for xenotransplantation in China

Background

Xenotransplantation has drawn increased attention in recent years as a potential solution to the scarcity of human source donor organs. Researchers have highlighted the need to characterize the influence of porcine endogenous retroviruses (PERV) in xenotransplantation. Screening and analyzing the presence and subtype of PERV in donor source animal breeds could provide basic parameters to evaluate the biological safety of xenotransplantation from pigs to humans. We bred a new miniature porcine herd (XENO-1) after decades of investigation, the herd was purpose bred to produce a potential donor animal source for xenotransplantation. To this end we studied the animals’ PERV expression characteristics.

Methods

We randomly selected 37 animals of the herd, PCR and RT-PCR based on specific primers were utilized to determine their PERV viral subtype. High fidelity PCR and restriction enzyme digestion were employed for variants detection. To thoroughly understand the PERV expression pattern, quantitative PCR was applied to measure mRNA expression levels in different tissues, At last, transfection capacity was assessed using a in vitro co-culture system.

Results

Our results revealed that the XENO-1 herd was free of PERV-C and exhibited low levels of PERVs in different tissues compared to commercial pig (landrace). The XENO-1 herd showed unique variants of A/B recombination. In addition, even though there were A/B variants in the XENO-1 herd, co-culturing revealed no evidence of PERV transmission from XENO-1 tissue to human cells.

Conclusion

Overall, Our results displayed an unique PERV expression pattern in a new pig herd and demonstrated its non-transfection capacity in vitro. Data in the research indicate that XENO-1 animals can serve as a better potential donor source for xenotransplantation.

Pig-islet xenotransplantation: recent progress and current perspectives

Islet xenotransplantation is one prospective treatment to bridge the gap between available human cells and needs of patients with diabetes. Pig represents an ideal candidate for obtaining such available cells. However, potential clinical application of pig islet still faces obstacles including inadequate yield of high-quality functional islets and xenorejection of the transplants. Adequate amounts of available islets can be obtained by selection of a suitable pathogen-free source herd and the development of isolation and purification method. Several studies demonstrated the feasibility of successful preclinical pig-islet xenotransplantation and provided insights and possible mechanisms of xenogeneic immune recognition and rejection. Particularly promising is the achievement of long-term insulin independence in diabetic models by means of distinct islet products and novel immunotherapeutic strategies. Nonetheless, further efforts are needed to obtain much more safety and efficacy data to translate these findings into clinic.

Porcine endogenous retrovirus (PERV) infection of HEK-293 cell line alters expression of human endogenous retrovirus (HERV-W) sequences

The risk of infections of human recipients after xenotransplantations is now mainly represented by porcine endogenous retroviruses (PERVs) as these particles are part of the porcine genome. As in all vertebrates, human genome harbours its own numerous genetic sequences of retroviral origin; it is estimated that they comprise about 8 % of the human genome. Because some of them play an important role in human physiology, it is valuable to estimate whether the presence of PERVs in human cells influences homeostasis of the human endogenous retrovirus (HERV) expression pattern. The aim of the study was to evaluate whether the expression profile of HERV-W genes changes after infection of cells by porcine endogenous retroviruses. In the experimental settings, human embryonic kidney cell line (HEK-293) was infected by PERV particles and cultivated up to 22th passage after infection. HERV-W gag, pol and env, as well as env from locus 7q21.2 gene expression was monitored by means of realtime reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot techniques. We found that the expression level of HERV-W genes differs in PERV-infected HEK-293 cell cultures in comparison with that from non-infected cultures. Relative HERV-W gene expression also differed significantly between particular passages (P < 0.05). Moreover, we have noticed a high correlation between the HERV-W Env(7q21.2) mRNA and protein level (Spearman rank r = 0.65; P < 0.05) during the course of the experiment. As previously hypothesized, human genomic sequences of retroviral origin may be changed by the presence of porcine endogenous retroviruses.

Knockdown of porcine endogenous retroviruses by RNA interference in Chinese experimental miniature pig fibroblasts

BACKGROUND

The clinical application of porcine-derived xenotransplants is limited by the potential risk of infection due to the presence of porcine endogenous retrovirus (PERV) in tissues, organs, and cells. The establishment of pig fibroblasts with low PERV expression and without PERV-C can provide a nuclear donor to generate a safer transgenic pig.

METHODS

In this study, we obtained Chinese Experimental Miniature Pig fibroblasts (CEMPF) with low expression of PERV and none of PERV-C. We designed small interfering RNA (siRNA) expressed as short hairpin RNAs (shRNA) based on the highly conserved gag and pol regions of PERV and screened for the most effective siRNA to inhibit PERV expression. The selected shRNA-pol3 fragment was introduced into the CEMPF to obtain an engineered CEMPF stably expressing shRNA-pol3.

RESULTS

The PERV mRNA expression level in the engineered CEMPF was only 7.9% of that observed in fibroblasts from wild-type CEMPF, PERV P15E protein expression was significantly reduced. HEK293 cells cocultured with the supernate of the engineered CEMPF showed no PERV infection.

CONCLUSIONS

Engineered CEMPF, which possess no risk of PERV-A/C infection, can serve as a nuclear donor to generate xenograft donor pigs.

Advances in research of pig islet xenotransplantation for diabetes

Pig islet xenotransplantation is effective in treating diabetes. Nowadays, the research of islet xenotransplantation is still in the research phase, and its clinical use is mainly restricted by the shortage of functional islets and graft rejection. In recent years, several studies have demonstrated the feasibility of successful preclinical pig islet xenotransplantation. Moreover, promising results concerning prolonged insulin independence were achieved with the improvement of islet isolation technologies, application of novel immunotherapeutic strategies, and the development of transplantation surgery. This review aims to elucidate the advances in the separation and preparation of transplanted pig islet, immunological rejection and treatments, potential safety problems, and clinical studies.